Pulse initiator



Sept. 9, 1958 F. WEST 2,851,635

PULSE INITIATOR Filed Sept. 16, 1954 2 Sheets-Sheet 1 a k M; JammingTIME SEC. M

POTEN Wwh 7M A TTORNEV Sept. 9, 1958 F. WEST 7 2,851,635

PULSE INITIATOR Filed Sept. 16, 1954 2 Sheets-Sheet 2 uvvavrop F. WES 7'B) a mM-ZQ A 7' TORNEV United States Patent fiice Patented Sept. 9.,1958 PULSE [NITIATOR Fred West, Chatham, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application September 16, 1954, Serial No. 456,572 6 Claims.(c1.31s-s4.s

duration called control pulses. Very often the first and :last device inthe cascade-are connected in the same mannor as successive devices inthe cascade, forming a closed ring which will continue operatingindefinitely in step With the applied control pulses. In such anarrangement it is generally preferable for all the bistable devices tobe identical and to be connected to their associated circuits in anidentical manner. This greatly simplifies the problem of achievingcontinuous operation of the ring. However, it is necessary to make someprovision to assure that a single preselected bistable device in thering is actuated on'the occurrence of the first control pulse.Thisrequirement has been recognized,and various special circuits andoperating procedures have beendevised in the attempt to meet it.

One such technique requires initial application of an unusually largecontrol pulse, capable of actuating one of the bistable devices inthe-ring even though the ring circuit is designed so-any device cannormally only be actuated by a control pulse after thepreceding devicein the'ring'has already been actuated by'the preceding control pulse.This technique has the disadvantage that more than one device may besimultaneously actuated, so thatadditionalrneans are needed toqu'icklydeactu-ate all This complicates the circuit and results nativeinitiating system utilizes a manual switch by which an operator canmomentarily apply a high potential to a selected bistable device,actuating it before the first'control pulse occurs. When the firstcontrol pulse occurs,

"the succeeding device in the cascade circuit is actuated.

This procedure requires that the operator know in adva'nc'e thatthefirst control pulse is soon to occur, and depends on the operator actingbeforehand. Theadvantage of a completely automatic initiating system isevident. Certain types of automatic initiating circuits have beendevised which are'applicable to circuits comprising cascaded bistabledevices wherein the potentialsapplied to and generatedby successivedevices in the cascade are all different. While such systems may besuitable where the circuit ceases operation after actuation of'the lastdevice in the cascade, they are unadapted to continuous operationof aclosedring.

An object of the instant invention is toprovide autoniatically operativemeans for initiating operation of a selected one of 'a cascade ofidentical bistable pulse actuated devices'on the occurrence of thefirstina series of con'trolpulses applied simultaneously to all devicesin thecas'cade.

A further object is to accomplish "the foregoing by means whichelectrically isolates itself from the cascade after having initiatedoperation of the selected bistable device.

A more particular object is to provide a ring of cascaded bistabledevices each of which contains an electric discharge tube controlled bya train of pulses applied simultaneously to all devices in the ring,whereby each discharge tube is rendered operative after the precedingone and becomes inoperative when the succeeding one is renderedoperative, and wherein only a single preselected discharge tube isrendered operative on occurrence of the first control pulse. 7

The invention attains these objects by utilizing an auxiliary bistabledevice which is either unbiased or biased to a much lesser degree thanthe'bistable devices in the ring circuit to be controlled. The controlpulses are applied to the auxiliary device as well as to all the devicesin the ring circuit. The auxiliary device therefore is actuated inresponse to the first control pulse. Each of the devices in the ringcircuit is initially in the deactuated state and is too heavily biasedto actuate in response-to any control pulse until the preceding devicehas been actuated. Actuation of the auxiliary device produces anenabling potential which is coupled through a condenser to a selectedone of the devices in the ring circuit. This causes immediate actuationof the selected device. The condenser quickly charges and thereafterblocks the enablingpotential from the ring circuit. The entire processoccurs so quickly that the selected bistable deviceis actuated at verynearly the instant of occurrence of the first control pulse.

A detailed description of a particular embodiment of the invention ispresented in. the following specification "inconjunctionwith theappended drawings in which:

Figjl is a drawing of the circuitof one suitable means 'for converting'atrain of square pulses to a train of positive controlpulses;

Fig. 2 is'an illustration of various waveforms involved inthe operationof the circuit in Fig. l; and

Fig. '3 is a drawing of the circuit of an embodiment offthe invention. 7v

The embodiment of the invention described hereinafter requires thatthecontrolpulses-utilizedfor actuating the ring circuit aIlbe shortduration positive potentials. When the pulses to "be utilized'as controlpulses-are of another configuration, since the sole function of thepulses is to'mark'the time intervals with which the ring circuit must besynchronized, it is a relatively simplematter for one skilled in the artto devise a suitable "pulse converting circuit to provide a series ofpulses of the required "type and spac'e'd'by the time intervals ofinterest'inthe original series 'of pulses. For'example,'suppose theoriginal series of'pulses aresquare in shape and of alternately risingand falling'potential. Such a pulse train is characteristically producedby telephone dialing circuits. In'Fig. l is shownone type 'of circuitwhich will convert such apulse train, designated at l, to a pulse trainof the desiredtype, indicated in Fig. '2(C). Pulse-train -1 is producedacross output terminals 2 and '3 of apulse source designated in block 4.Terminal 3 is grounded. Terminal 2, in one path, is connected to outputterminal 5 through the series connection of condenser 6 and diode "7,with diode 7, poled so'as to present low resistance to current flowtoward terminal 5. A grounded resistor 8 is connected to the junction-ofcondenser 6 and diode 7. Condenser 6 and resistor 'Sare chosen to have asmall time constant relative' to the smallest time interval of interestin pulse train 1. They therefore serve as a differentiating circuit, thevoltage across resistor 8 closely approximating the time derivative ofthe voltage at terminal 2. With diode 7 connected as described,'only the'positively" rising "portions ofthis time "derivative will be conveyedto terminal 5. The potential at terminal 5 due to the circuit so fardescribed will have a waveshape of the type shown in Fig. 2(A). Eachsharp rising portion occurs at the instant of the rising portion of eachpulse in waveshape 1.

Terminal 2, in another path, is connected to the gridof a triode 9serving as a polarity inverter. The plate of triode 9 is connectedthrough a resistor 10 to a source of positive direct-current potentialB+. The cathode is grounded through a self-biasing resistor 11. Thepotential at the plate of triode 9 will be of the same shape as thepotential applied to the grid, but of opposite polarity. The plate isconnected to the grid of another triode 12 serving as a cathodefollower. Triodes 9 and 12 may conveniently be in a single envelope. Theplate of triode 12 is connected to source B+. The cathode is connectedto ground through a resistor 13. The potential at the cathode will be ofthe same shape and polarity as the potential applied to the grid, butthe low output impedance of a cathode follower is more effective forcoupling this potential to a differentiating circuit than directcoupling from the plate impedance of triode 9. The cathode of triode 12is connected to output terminal 5 through the series connection ofcondenser 14 and diode 15, the latter poled so as to present lowresistance to current flow toward terminal 5. A grounded resistor 16 isconnected to the junction of condenser 14 and diode 15. Condenser 14 andresistor 16 serve as a differentiating circuit, and diode 15 onlypermits the positively rising portions of the time derivative voltageacross resistor 16 to be conveyed to terminal 5. The potential atterminal 5 due to this circuit will therefore have a waveshape of thetype shown in Fig. 2(B). Due to the polarity inversion produced bytriode 9, each sharp rising portion of that waveshape occurs at theinstant of the falling portion of each pulse in waveshapc 1.

If the first pulse in waveshape 1 is a rising portion, the first pulseat terminal 5 will be the first pulse in the waveshape in Fig. 2(A). Thesucceeding pulse in waveshape 1 will be a falling portion, so that thenext pulse at terminal 5 will be the first pulse in the waveshape inFig. 2(B). This process cyclically continues in response to successivepulses in waveshape 1, and the resultant time variation of the potentialat terminal 5 will be the sum of the pulses in Figs. 2(A) and 2(3), andis shown in Fig. 2(C). Since this is a train of positive pulses, withthe intervals between pulses marking the time intervals of interest inwaveshape 1, it is the desired result.

Referring now to Fig. 3, there is illustrated the circuit of a preferredembodiment of the invention. In block 104 is designated a source ofpositive polarity control pulses 17 of the same general type as thoseillustrated in Fig. 2(C). Pulse source 104 has output terminals 102 and103, of which terminal 103 is grounded. A ground return resistor 21 isconnected between terminal 102 and ground. Terminal 102 is alsoconnected to a control pulse conductor 22 which conveys the controlpulses to each of a plurality of electrical bistable devices I, II, N.These devices are connected in cascade,with the first coupled back tothe last to form a continuous ring. There may be any number of suchdevices, and since they are identical and are connected identically adetailed description of device I will serve for all.

Device I includes a gaseous electric discharge tube 23 having an anode,a cathode and a control electrode. Tube 23 is of the type in whichconduction, or discharge, from anode to cathode starts and continuesafter a suitable voltage is applied to the control electrode, and ceaseswhen the anode potential is sufficiently reduced. The starting ofconduction is called firing. Preferably, but not necessarily, thecontrol electrode is a grid structure, and a shield grid is included inthe tube to reduce the current flow to the control grid when the tubefires. Such tubes are well known and are commercially available. Theshield grid is connected to the cathode, which is connected to groundthrough the series connection of resistors 24 and 25. A condenser 26shunts these resistors. The control grid is connected to pulse conductor22 through a diode 27 poled to present low resistance to current flowfrom conductor 22 toward the control grid. The control grid is alsoconnected to a source of negative direct-current potential E- through aresistor 28. The anode of tube 23 is connected through a resistor 29 toa source of positive potential B+. Source 3+ may be disconnected fromall bistable devices I, II, and N by opening a switch 30, therebyrestoring all tubes, including tube 35, to their nonconducting state.The coupling of device I to device 11 consists of a resistor 31connecting the cathode of tube 23 to the control grid ofanother'discharge tube 23' in device II, and a condenser 32 connectingthe anodes of both tubes. The output potential of device I appears atthe cathode of tube 23, and the portion of it existing across resistor25 is made available by output conductor 33 connected to that resistor.

To explain the operation of the ring circuit reference will be made totwo adjacent devices I and II. All elements of device II serving thesame function and connected in the same way as corresponding elements ofdevice I have been designated with the same identifying numeral but witha prime superscript. Until tube 23 is conducting, the bias applied bysource E to the control grid of the succeeding tube 23' is sufficient sothat the latter tube cannot fire even though control pulses are appliedto its control grid from pulse conductor 22. Suppose tube 23 has beenrendered conductive by means hereinafter described. The resultantcurrent flow through resistors 24 and 25 produces a positive potentialat the cathode. A fraction of this potential determined by the voltagedivider comprising resistors 31 and 28' is applied to the control gridof tube 23'. This reduces the effective bias of the control grid sothat, on occurrence of the next control pulse, tube 23 fires. Diode 27'serves to prevent the positive cathode potential of tube 23 fromreaching pulse conductor 22, which might result in out-of-turn actuationof another bistable device in the ring circuit. The firing of tube 23'causes a sharp drop in its plate potential due to current flow throughresistor 29, and this potential drop is conveyed as a large negativepulse to the plate of tube 23 by condenser 32. The net plate potentialof tube 23 drops below the level required to sustain conduction, and thetube extinguishes. This process occurs very rapidly, tube 23 beingextinguished practically at the instant that tube 23' fires. The portionof the cathode potential of tube 23' appearing across resistor 25 ismade available by output conductor 33, and constitutes the output oftube 23. This potential appears when the tube fires, remainssubstantially constant, and ends when the tube is extinguished at theoccurrence of the succeeding control pulse. Condenser 26 serves to slowdown the rate of rise of potential of the cathode of tube 23', since toosharp a voltage pulse at the cathode would result in transient voltagesthat could trigger the tube in the succeeding bistable device in thering circuit in a random manner.

As a result of this construction and mode of operation of the ringcircuit, device I will produce an output potential during the intervalthat tube 23 is conductive, device II will produce an output potentialduring the interval that tube 23 is conductive, and similarly for allother devices in the ring circuit. These output potentials appear atoutput conductors 33, 33', etc. in succession. They may be utilized formany well-known applications, including, for example, use in gategenerators, distributors, and time division multiplex transmissionsystems. Patent 2,485,886, issued October 25, l949, to C. W. Johnstoneet al. illustrates a system of the latter type wherein the function ofthe Gating switch could obviouslybe performed; by "connecting outputleads 33, 33', "are. to the "respective "ftr'a'nsmitters.

The above description (if the c'ir'cuitin Fig. 3 proceeded "on 'theasshmption' 'thajt one device in the ring circuit had already beenactiiated. The manner in which a selected device, device I, is actuated'on occurrence of thejfirst control piilse willnow b'e'explained. Anauxiliary"tube 35, which maybe 'o'fthe sametyp'e as tube 23, has itscontrol grid connected to bUtputter'minal 102 of pulse source 104through, "the series combination of a condenser 36 and a 'diode'3 7.Diode 37 is poled to between giroundarid th'e' junctionoftlioseresistors. The cathodeof 'tub'e 35is connected to the control grid oftube 23 in device I through the series connection of a diode 44 and acondenser 45, diode 44 poled to present low resistance to currentflowing toward the control grid of tube 23. Diode 44 has a reverseresistance of a few megohms, and may conveniently be a crystalrectifier.

Before any control pulses have occurred, all tubes in the circuit aremade nonconductive by momentarily opening switch 30. At the instant thefirst control pulse occurs, it will be conveyed through condenser 36 anddiode 37 and will return to ground through resistor 38. The resultantpositive potential across resistor 38 is enough to fire tube 35 since ithas a relatively small applied cathode bias. Diode 37 limits thetransient voltage fed back to pulse source 104 when positive ion gridcurrent starts as a result of firing tube 35. Condenser 36 prevents thesteady state grid current flowing after the firing of tube 35 fromintroducing an unwanted bias voltage in pulse source 104. Condenser 43is provided because when switch 30 is first closed, before the firstcontrol pulse, a transient surge voltage is initiated from source B+.This transient may appear at the grid of tube 35 with sufiicientmagnitude to inadvertently fire it because of its relatively low bias.Condenser 43 delays the rise of 13-}- potential at the anode of tube 35for a sufiicient time for the transient voltage to die out. Itthereafter remains charged and has no further eifect on the circuit.

The firing of tube 35 suddenly raises the potential of its cathode, andthis sharp positive surge voltage is conveyed through diode 44 andcondenser 45 to the control grid of tube 23. Tube 23 therefore fires.The cathode potential of tube 35 thus serves as an enabling potentialfor tube 23. The entire process occurs very rapidly, tubes 35 and 23firing almost together at the instant of occurrence of the first controlpulse. Condenser 45 is charged rapidly by the cathode potential of tube35 through a path from the cathode, through diode 44, condenser 45,resistor 28, source E and cathode resistor 40. Hence, the cathodepotential of tube 35 is thereafter blocked and has no further effect onthe operation of tube 23. Diode 44 prevents control pulses conveyed tothe control grid of tube 23 from being dissipated in the circuitry oftube 35. Diode 44 and condenser 45 thus serve as means for blocking theenabling potential from reaching device I after that device hasresponded to the first control pulse.

When it is desired to reset the complete circuit to' startingconditions, switch 30 may be momentarily opened. This removes the platepotential from all of the tubes, causing all of them to extinguish.

While the particular embodiment of the invention de- "shown.

6 scribed above utilizes a gaseous discharge tube circuit as each ofthebistable elements i'n'the' ring circuit, it is evident that anydevice capable of being switched from a nonconductive to a conductivecondition and back again 'to the nonconductive condition by properlyapplied voltage pulses would 'besuitable. For example, a bistablemultivibrator using high vacuum tubes, wherein only one tube isutilizedas 'a source of output pulses, would providesuch acharacteristic. In addition, the only basic requisite of th'e'auxiliary'tube is that it actas a switch which is open until a control pulsecauses it to close and stay closed. This behavior could be attained by alock-down type of relay circuit, which therefore could readily beadapted to"se"rveas a substitute for the tube The discharge tube ispreferred, however, because of its greater speed of response to appliedpulses, its high sensitivity, and "general superior compatibility withthe circuitry involved.

What is claimed is: d

1. In combinationfa ring circuit or identically interconnecteddischargetubc'seach of'which has a control electrode, acathodefand "ananode, each of said discharge tubes"h'aviti jejxting uisjhedandconductive stable states, a common 'p'ulsecoiiductor connected to saidcontrol electrodes of said tubes to convey successively applied controlvoltage pulses of the same polarity, a resistor connecting the cathodeof each tube to the control electrode of the succeeding one of saidtubes in said ring circuit, a bias source connected through impedancemeans to each control electrode, said source having a voltage sufiicientto permit conduction by a tube upon receipt of said control pulses onlywhen its preceding tube in said ring is conducting, a capacitiveconnection between said anodes of successive ones of said tubes adaptedto cause the preceding one of said tubes to ex tinguish substantially atthe instant that the succeeding one of said tubes becomes conductive, anauxiliary discharge tube having a cathode and a control electrode, meansconnecting said auxiliary tube control electrode to said common pulseconductor, said auxiliary tube having an extinguished and a conductivestable state, and a capacitive connection between the control electrodeof a selected one of said tubes in said ring circuit and said cathode ofsaid auxiliary tube.

2. The combination described in claim 1, wherein said means connectingsaid control electrode of said auxiliary tube to said pulse conductorcomprises a capacitor and a device presenting low resistance to currentfiow in a direction toward said control electrode and high resistance tocurrent flow in the reverse direction.

3. In combination with a ring circuit of the type comprising a pluralityof pulse responsive bistable devices so interconnected as to beindividually actuated in succession in response to occurrence ofsuccessive pulses in a series of pulses applied to said ring circuit,biasing means adapted to apply a biasing potential to all of saiddevices whereby all are initially deactuated and insensitive to saidpulses, initiating means comprising an initially nonconductive electricdischarge tube, an input circuit and an output circuit therefor, meansfor applying said series of pulses to said input circuit whereby saidtube becomes and remains conductive in response to the first of saidpulses to generate an enabling potential in said output circuit, meansincluding a capacitor in series with an asymmetric conductive deviceconnecting said output circuit to a selected one of said devices wherebysaid enabling potential overcomes said biasing potential and actuatessaid selected device substantially at the time of occurrence of saidfirst pulse.

4. In combination, a chain of bistable devices adapted to be connectedto a source of pulses of like polarity, each of said devices constructedand arranged to change from a first to a second stable state in responseto a pulse occurring after the preceding device in said chain has sochanged in response to the preceding pulse, each of said devices furtherconstructed and arranged to change from said second to said first stablestate in response to the changing of the succeeding device in said chainfrom said first to said second stable state, a bias means for saiddevices to render all of them initially unresponsive to said pulses, anauxiliary bistable device comprising an electron discharge device havinga normally nonconductive state and a conductive state, a cathode and acontrol electrode in said device, means for coupling said controlelectrode to said source of pulses whereby said auxiliary device changesto its conductive state upon receipt of the first pulse, a connectioncomprising imped ance means between said cathode and a selected one ofthe bistable devices in said chain whereby said selected device changesstate in response to a pulse from said cathode.

5. Means for initiating operation of only a selected one of a ringcircuit of bistable electron discharge devices of the type wherein eachdevice is caused to operate in sequence in response to a series ofcontrol pulses, said means comprising means for initially setting all ofsaid devices to the same one of their two stable states, means forsimultaneously supplying control pulses to each of said devices, biasingmeans connected to each device rendering them unresponsive to saidpulses while all are set to said one stable state, an auxiliary bistabledevice including an input electrode and an output electrode, means forconnecting the input electrode to said means for supplying controlpulses whereby said auxiliary device is caused to change state uponreceipt of the first control pulse, and a connnection from said outputelectrode to the selected bistable device in said ring ring circuitwhereby the operation of said ring circuit is initiated by the operationof the selected device in response to the first control pulse.

6. The combination of claim 5 wherein the connection from said outputelectrode comprises a capacitor and an asymmetric conductor connected inseries.

References Cited in the file of this patent UNITED STATES PATENTS2,398,771 Compton Apr. 23, 1946 2,485,886 Johnstone et a1. Oct. 25, 19492,730,658 Six Jan. 10, 1956 2,739,235 Sande Mar. 20, 1956 2,743,394Ruhlig Apr. 24, 1956 2,758,250 Ridler et al Aug. 7, 1956

